The present invention relates to an extraction device for separating the liquid components from solid components in a liquid-solid mixture.
A known extraction device comprises a drivable screw which is rotatable in a press barrel, a screw flight helically disposed thereon, and radially extending pins which extend into the press barrel in the direction of the screw axis. The pins extend substantially to this axis although their depth of penetration is adjustable. Gaps are formed in the flights which correspond to the diameter of the pins.
In U.S. Pat. No. 3,981,658, there is disclosed a device for extracting liquids from solid-liquid mixtures which has pins protruding through the press barrel. Such pins extend radially to the screw and prevent the material to be extracted from rotating with the screw. Such pins cause an adequate conveying pressure to be built up.
The present invention seeks to provide an extraction device whereby extracted liquid may be discharged directly from the site at which it is extracted without a substantial drop in pressure occurring due to such discharge. This pressure drop occurs in known filter presses.
According to the present invention, there is provided an extraction device for separating liquid components from the solid components of a liquid-solid mixture, comprising a drivable screw rotatable in a press barrel, a screw flight helically disposed on the screw and a plurality of radially directed pins which extend into the press barrel and are directed towards the longitudinal axis of the screw, the pins extending substantially to the base of the screw thread, the screw flight having a plurality of gaps formed therein, the gaps being so dimensioned that, in an axial direction, the width of the gaps corresponds to the diameter of the pins, wherein an axially extending bore is formed in each pin, the bores being open in the direction of the longitudinal axis of the screw and being in communication with a network for the discharge of the extracted liquid component.
The provision of discharge bores extending axially in the pins and which are open in the direction of the screw axis and which are connected to a discharge network enables the extracted liquid to be discharged at the site at which it is produced, without a substantial pressure drop being caused by the discharge apertures.
The pins prevent the material from rotating with the screw, so that a high conveying output is achieved and consequently a high pressure is built up in the pin-barrel region. Because of the high pressure, the water contained in the cells of the solid components of the material can be extracted. Accordingly, beet leaves, beet slices and sludge can be extracted, the liquid being released and easily discharged through the discharge bores formed in the pins. This is because there is a high drop in pressure of, for example, from 300 bars which is the pressure in the press barrel and 1 bar (atmospheric pressure) in the discharge bores.
Since the spacing of the tips of the pins from the bottom of the screw thread is relatively small, for example in a practical arrangement 0.3 mm, it is also possible for minute solid particles, which do not block the discharge bores, to be simultaneously discharged. The tips of the pins are adapted to the rounded shape of the core of the screw.
Advantageously, the pins are located between helical portions of the flights, the flights having radially extending bores formed therein, the radial bores being connected to an axial bore formed in the interior of the screw.
Such a measure makes it possible for the extracted liquid lying in the bottom of the screw thread to pass into the discharge bores formed in the pins and for the extracted liquid located adjacent the internal surface of the barrel to be discharged over the flight ridges, through the radial bores in the flights and into the axial bore in the screw. Such an arrangement means that substantially all of the extracted liquid is immediately collected and discharged whilst no substantial drop in pressure occurs in the barrel itself due to the discharge of the liquid.
Desirably, the press barrel has at least one region provided with at least one internal groove, the pins being located in the at least one grooved region. Such internal grooves are, for preference, axial grooves but may also be helical grooves corresponding to the pitch of the flights or extending in a direction counter to the pitch of the flights. The grooves may be triangular, rectangular or semi-circular in cross-section.
Preferably, a plurality of pins are combined to form a pin plane, the individual pins in each plane being disposed at equiangularly spaced intervals around the periphery of the press barrel, each pin being capable of being screwed into the press barrel and the depth of insertion of the pins into the barrel being adjustable.
Such an arrangement also makes it possible for the conveyance of the material to be maintained between the individual pin planes, because the grooves in the barrel prevent the material from rotating with the press screw. Because of this intensified conveying effect, a high pressure is produced which is essential for effective extraction. A high enough pressure enables the water contained in the cells of the solid components to be released and consequently permits high dry-substance contents to be achieved in a single operation in a continuous manner. Such an arrangement also ensures that the extracted liquid is discharged at the site where it is extracted without any substantial drop in pressure occurring in the barrel.
The combination of a plurality of pins, each provided with a discharge bore, to form one or more pin planes, makes it possible for the extracted liquid to be extracted peripherally at a plurality of locations. The adjustability of the pins with regard to their depth of insertion does, of course, produce a change in the conveying output and hence a change in the build-up of pressure. However, it permits the extraction device to be adapted to extract liquids from mixtures in which the solid components are of different sizes.
Further advantageously, the pins each have a tip portion capable of sliding on the base of the thread of the screw, the tip portions being made of a material having dry-running properties. Thus, the tips may be made of bronze. This ensures a long, relatively wear-free useful life for the tips of the pins.
Further desirably, small-bore tubes are inserted into the end region of discharge bores formed in the pins facing the screw, the tubes being conically inwardly tapering in a direction towards the screw. This makes it possible for the inlet apertures of the bores to be of small diameter. Such a measure counteracts the blocking of the bores in the pin bores and hence in the discharge system in communication therewith.
Further preferably, at least the portions of the pins which extend into the interior of the press barrel are of rectangular or polygonal cross-section. Such an arrangement provides a shearing effect which causes the cutting-up of solid particles as the particles are conveyed between the gaps in the flights and the pin members.